1. Field of the Invention
The present invention relates to, in a technology for exposing electron beams (EB-exposure) onto a semiconductor wafer, a mask for electron beam exposure in which the proximity effect correction method is improved, a manufacturing method for the same, and a manufacturing method for a semiconductor device using the same, and in particular to a mask for electron beam exposure being preferable as a stencil mask for a projection exposure apparatus in which the entirety or a part of a pattern corresponding to one chip is formed, a manufacturing method for the same, and a manufacturing method for a semiconductor device using the same.
2. Description of the Related Art
FIG. 1 is a drawing showing an electron optics of EB projection exposure apparatus. In this EB projection exposure apparatus, stencil mask 21 with openings formed at portions for transmitting electron beams, projection lens 22, limiting aperture 23, and object lens 24 are disposed in parallel to each other so that their center axes are matched with each other, and under the object lens 24, wafer 25 is disposed.
On the surface of the wafer 25, resist film 26 is formed, and onto the resist film 26, electron beams transmitted through the openings in the stencil mask 21 are converged by the projection lens 22, narrowed by the limiting aperture 23, and further converged by the object lens 24, and then irradiated. In the stencil mask 21, a pattern or a part of the pattern corresponding to one chip is formed, and by scanning electron beams onto the stencil mask 21, a pattern corresponding to one chip is exposed on the resist film 26 on the wafer 25.
Thus, in the EB-exposure technology, a pattern is written onto a resist film formed on a mask material by electron beams, developed, and etched to form a mask for electron beam exposure (mask-writing), and furthermore, by using this mask for electron beam exposure, electron beams are exposed to transfer the mask pattern onto the resist film on the wafer (wafer-writing). These cases have a problem whereby, due to a so-called proximity effect, the pattern line width deviates from the designed width, and therefore, mask-writing and wafer-writing are carried out by a pattern in which such a dimensional change due to the proximity effect is corrected.
That is, the proximity effect is a dimensional change caused by unevenness in pattern density, which is a phenomenon, wherein, in a case where a pattern as a target to be formed on a wafer has lines with fixed widths aligned at fixed spaces, if a negative type resist is used, the widths of the lines at both sides of the pattern become smaller than that of the normal portion at the pattern center section. This dimensional change due to the proximity effect occurs when electron beams which are transmitted through the resist film and enter inside the Si substrate are made incident again onto the resist film due to backscattering. Therefore, the sections of the resist film and Si substrate are cut into meshes. Energy deposited in the resist film due to irradiation of electron beams is calculated by a computer for each mesh. The energy distribution due to the proximity effect is simulated using an exposure intensity distribution (EID) function and is determined. By this EID function, as shown in FIG. 2, the proximity effect correction exposure dose for wafer-writing is pre-determined in accordance with the distances from the pattern end portions. By using the determined amounts as mask bias amounts, pattern dimensions of the mask for electron beam exposure are determined. The mask bias amounts make up for the decreased amounts of the line widths due to the proximity effect by increasing the exposure dose at the pattern end portions at which the line widths become smaller, whereby the decreased amounts of the resist dimensions at the pattern end portions are estimated, and the estimated amounts are added to the designed widths as bias amounts for correction.
Also, the distribution of the energy deposition due to forward scattering electrons which have directly entered from the outside into the resist film and backscattering electrons which re-enter into the resist film after scattering inside the Si substrate is as shown in FIG. 3, and this deposited energy distribution is expressed by the exposure intensity distribution (EID) function shown by the following Formula 1.
f(r)=k{exp(xe2x88x92r2/xcex2f2)+xcex7(xcex2f2/xcex2b2)exp(xe2x88x92r2/xcex2b2)}xe2x80x83xe2x80x83(1)
In the above formula, r is the distance from the irradiating point, xcex2f is the range of the deposited energy distribution due to forward scattering as shown in FIG. 3, xcex2b is the range of the deposited energy distribution due to backscattering, and xcex7 is called a reflection coefficient which is a constant determined depending on the substrate material.
Thus, in order to correct the dimensional change due to the proximity effect, in the prior-art, the mask bias (the correction dose of the mask pattern) is determined by a numerical operation using the EID function and meshes, and the mask in which this mask bias is taken into consideration is used to expose electron beams onto a wafer. Likewise, when manufacturing a mask for electron beam exposure, in order to correct the proximity effect due to electron beams, a numerical operation is carried out, and based on an obtained correction exposure dose, electron beams are exposed onto the resist film on the mask material, whereby a mask is manufactured. Therefore, in the prior-art, the operation is carried out twice when manufacturing a mask and wafer-writing to correct the proximity effect.
However, since the correcting operations are performed for each of the divided meshes, complicated calculation processing is required, and therefore, correcting accuracy is low. In order to increase the correcting accuracy, the mesh size may be made smaller, however, if so, the time required for calculation becomes significantly longer, the processing takes considerable time, and throughput is lowered.
Therefore, a proximity effect correcting method has been proposed for the purpose of omitting the proximity effect correction exposure process for each wafer, and forming a high density pattern at high throughput (Japanese Laid-Open Patent Publication No. Hei-10-90878). In this proximity effect correction method, a mask substrate applied with a resist is prepared, a mask pattern is written onto the substrate resist film by means of EB-exposure, and by using a proximity effect correction mask separately prepared, correcting exposure of the pattern transferring mask is carried out. At this time, the pattern and exposure dose of the correcting mask are determined so that the pattern formed on the mask is additionally corrected (excessively corrected) for the proximity effect which will occur when EB-exposure onto a wafer later, and then, the pattern is developed and etched, whereby a pattern transferring mask whose proximity effect has already been corrected is obtained, and by using this mask, EB are exposed onto the wafer by means of transferring and exposing once. Thereby, two exposure processes including correcting exposure onto each wafer are required for exposure onto the wafer in the prior-art, however, correcting exposure is carried out during manufacturing a mask, whereby a mask whose proximity effect has already been corrected is manufactured, and by omitting the correcting exposure process for wafer-exposure, wafer-writing can be completed by the exposure process once to improve throughput.
However, also in this prior-art, as in the previous case of the prior-art, correction of the proximity effect due to electron beams when mask-writing and correction of the proximity effect due to electron beams when wafer-writing are required, and therefore, the correcting processing takes considerable time for calculation, and also, the problem of low calculation accuracy still remains.
It is an object of the present invention to provide a mask for electron beam exposure whereby the calculation accuracy can be improved, and a manufacturing method for the same, and a manufacturing method for a semiconductor device using said mask.
The mask for electron beam exposure according to the present invention is formed from the same material as that of a wafer to be exposed, and the mask has a writing pattern accompanying a correction dose twice the proximity effect correction dose in mask-writing. This writing pattern is formed by means of patterning with use of electron beams at the same accelerating voltage as in wafer-writing.
This mask for electron beam exposure is, for example, a stencil mask having openings for transmitting electron beams, or a membrane type mask having a very thin film. Also, in this mask, for example, the entirety or a part of a pattern corresponding to one chip is formed for use in a projection exposure apparatus.
The manufacturing method for a mask for electron beam exposure according to the present invention comprises the steps of calculating the proximity effect correction dose in mask-writing, exposing onto a resist film formed on the surface of a mask material which is the same material as that of a wafer to be exposed by a pattern accompanying a correction dose twice the proximity effect correction dose in mask-writing at the same accelerating voltage as in wafer-exposing, forming a resist film pattern by developing the resist film, and forming a mask by etching the mask material with use of the resist film pattern as a mask.
In this manufacturing method for a mask for electron beam exposure, for example, the mask material is an SOI (silicon on insulator) adhered substrate having an Si film formed on an SiO2 film on an Si substrate, which is formed so that a resist film pattern is formed on the Si film, and the Si film is etched by using the resist film pattern as a mask. As a mask, a so-called hard mask in which the SiO2 film formed on the Si film is etched by using the resist film may be used. Also, after etching the Si film, it is preferable that a process in the area matched with the patterning portion of the Si film on the Si substrate is etched and removed to expose the SiO2 film is provided.
The manufacturing method for a semiconductor device according to the present invention comprises the steps of calculating the proximity effect correction dose in mask-writing, exposing onto a resist film formed on the surface of a mask material which is the same material as that of a wafer to be exposed by a pattern accompanying a correction dose twice the proximity effect correction dose in the mask-writing at the same accelerating voltage as in wafer-writing, forming a resist film pattern by developing the resist film, forming a mask by etching the mask material by using the resist film pattern as a mask, and exposing electron beams onto the resist film on the wafer at the same accelerating voltage as in the mask-writing by using said mask.
In the prior-art, in stencil mask manufacturing is processes, when mask-writing by means of electron beams, a device whose cost is relatively low is used for exposure at a relatively low accelerating voltage of approximately 20 through 50 kV. On the other hand, when wafer-writing by using this stencil mask, in order to increase throughput, it is necessary to increase electric current for the electron beams, and in order to prevent resolution from lowering due to the Coulomb interaction effect when increasing the beam current, the accelerating voltage is also increased, for example, to 50 kV or 100 kV to increase resolution.
The present invention is made by paying attention to points that the proximity effect depends on the accelerating voltage of the electron beams, and is influenced by the material of the substrate disposed under the resist film to be exposed. In other words, the exposure intensity distribution of electron beams is expressed by using the xcex2f, xcex2b and constant xcex7 as shown in the above mentioned Formula 1, and the xcex2f and xcex2b depend on the accelerating voltage of the electron beams and constant xcex7 depends on the substrate material. Therefore, the change in line width due to the proximity effect varies depending on the accelerating voltage, and if the accelerating voltage is the same, the proximity effect is also the same. Also, the proximity effect is caused by backscattering by which electron beams transmitted through the resist film scatters inside the substrate under the resist film, and the scatting beams are made incident onto the resist film again. Therefore, the degree of the change in line width due to the proximity effect is determined depending on the material of the substrate under the resist film.
Therefore, in the invention, the mask material is the same material as that of a wafer to be exposed, and a resist film formed on this mask is exposed at the same accelerating voltage as in wafer-writing, and patterning is carried out for the resist film. And, an amount for correction of the proximity effect when mask-writing is operated to determine a mask bias, and this correction dose is doubled for writing onto the mask. This doubled correction dose results by adding amounts to increase the writing line widths at the pattern end portions when mask-writing and when wafer-writing so that the line widths which are decreased due to the proximity effect when mask-writing and wafer-writing are corrected. Therefore, if the writing onto the wafer is carried out by using this mask without correction at the same accelerating voltage as in mask-writing, a pattern with line widths following the designed widths is written. In the present invention, the operation for the correction dose is carried out only once, whereby the calculation time is shortened, and furthermore, if it is supposed that the calculation time is the same as in the prior-art, the calculation accuracy can be remarkably improved by making the meshes extremely fine.